1. Field of the Invention
This invention relates to a control device for a vehicular engine having an automatic transmission and its control method for controlling an output of an engine when a speed is changed by an automatic transmission in a vehicle having the automatic transmission.
2. Discussion of Background
FIG. 19 shows the construction of a conventional control device for a vehicular engine having an automatic transmission, which is disclosed, for instance, in Japanese Examined Patent Publication No. 20164/1991, wherein a reciprocating piston 23 is inserted into an engine main body 1 and a combustion chamber 24 is formed above the piston 23. An intake pipe 10 and an exhaust pipe 13 are respectively connected to the combustion chamber 24. A throttle valve 12 is provided upstream of the intake pipe 10. An injector 11 is provided downstream of the intake pipe 10 such that the injector 11 protrudes into the intake pipe 10.
Furthermore, although not described in the publication, in addition to these, an intake air quantity sensor or a boost pressure sensor for detecting an inner passage pressure of the intake pipe 10 may be provided upstream of the throttle valve 12. An ignition plug 15 is disposed in the combustion chamber 24 such that the ignition plug 15 protrudes in the combustion chamber 24. Furthermore, a crank angle sensor 18 for detecting an engine crank angle and an intake stroke TDC is provided at the crank shaft 31 connected to the piston 23 and rotating cooperatingly therewith.
The throttle valve 12 is connected with a throttle opening degree sensor 19, a servomotor 19b for driving the throttle valve 12 and a servomotor driving circuit 19a for driving the servomotor 19b. An accelerator opening degree sensor 101 for detecting an operating quantity of an accelerator pedal, that is, an accelerator opening degree, is provided to the accelerator pedal, not shown. A stroke sensor 102 is provided to a car body for detecting a sinking quantity of a suspension, not shown, for the purpose of detecting a car weight.
On the other hand, an automatic transmission 4 is provided with a gear position sensor 64 for detecting speed changing steps of a gear changing unit 43, a rotation speed sensor 62 for detecting a rotation speed of an output shaft of a torque converter 3, a vehicle speed sensor 63 for detecting a vehicle speed from a rotation number of a driving shaft, not shown, and a hydraulic control unit 5a for switching operational combination of a plurality of hydraulic friction elements 42 provided in the automatic transmission 4 for conforming the gear changing unit 43 to speed changing steps in accordance with the running state of a car.
An electronic control unit (ECU) 6 receives detecting signals from sensors for detecting various running conditions of the engine, for instance, detecting signals from an intake quantity sensor, the throttle opening degree sensor 19, the crank angle sensor 18 and the like, or a speed changing signal of the automatic transmission 4 or the like, controls starting of fuel injection and a valve opening time of the injector 11 in accordance with a previously memorized program, and controls current flowing timing and a current flowing time of discharge energy to the ignition plug 15 through the ignition coil 16. The ECU 6 controls the intake quantity by controlling the throttle opening degree through the servomotor 19b such that the output torque of the engine can be provided in accordance with an operating quantity of the accelerator pedal. The ECU 6 performs the speed changing control by outputting a control signal for switching the operational combination of the hydraulic friction elements to a new combination in accordance with the speed changing step, to the hydraulic control unit 5a such that the speed changing step of the gear changing unit 43 of the automatic transmission 4 is optimized in accordance with a vehicle velocity provided by a vehicle velocity sensor 63 and the above running conditions of the engine.
The ECU 6 is composed of a CPU, a ROM, a RAM, an A/D converter having a multiplexer, an I/O interface circuit, a common bus connecting these and the like. The CPU calculates a fuel injection quantity based on the data detected by the various sensors in accordance with a program memorized in the ROM, and outputs a pulse signal based on the calculated fuel injection quantity to the injector 11 through a driving circuit in the I/O interface circuit. At this occasion, the fuel injection quantity TAU.sub.0 is determined based on the following equation (1). EQU TAU.sub.0 =TP.multidot.FAF.multidot.K+TV (1)
where TP designates a basic injection quantity determined by a ratio A/N=Q.sub.a /N.sub.e of the intake quantity Q.sub.a as compared to the rotation speed N.sub.e of the engine, FAF, an air-fuel ratio correction coefficient, K, other correction coefficient and TV, an ineffective injection time due to the operational delay of the injector 11. Furthermore, the ignition time SA.sub.0 is calculated by a table look-up of an advance angle map which is previously determined by the rotation speed N.sub.e of the engine and the A/N value. The ignition timing and the current flowing time are controlled through the ignition signal driving circuit in the I/O interface circuit based on the calculated value.
Furthermore, the ECU 6 predicts by calculation a target engine torque T.sub.er by the following equation (2), in accordance with the signals from the various sensor for detecting the various running conditions of the engine. EQU T.sub.er =K.sub.1 .multidot.a-K.sub.2 .multidot.N.sub.e ( 2)
where K.sub.1 and K.sub.2 designate parameters for determining a characteristic of the output torque of the engine, wherein K.sub.1 is a proportional coefficient of the output torque of the engine with regards to the accelerator opening degree "a" and K.sub.2, a proportional coefficient of the output torque with regards to the rotation speed N.sub.e of the engine, which are respectively calculated by the following equation (3). EQU K.sub.1 =C.sub.1 .multidot.W/m, K.sub.2 =C.sub.2 .multidot.W/m.sup.2( 3)
where m designates a gear ratio (speed reducing ratio) of the gear changing device 43, C.sub.1 and C.sub.2, constants which are previously obtained by experiments or the like and which provide the best driving feeling of the vehicle and W, vehicle weight provided by the following equation. EQU W=W.sub.0 +x/k.sub.s ( 4)
where W.sub.0 designates a previously-known weight of only the car body, x, an output of the stroke sensor 102 which is a sinking quantity of the suspension caused by the weight of passengers or a mounted load and K.sub.s, a spring constant of suspension.
Furthermore, the target throttle opening degree which provides the intake quantity necessary for outputting the target engine torque T.sub.er, is read from a throttle opening degree table by the rotational speed N.sub.e of the engine and the target engine torque T.sub.er, which is outputted to the servomotor driving circuit 19a. The servomotor driving circuit 19a drives the servomotor 19a positively and negatively in accordance with a deviation between the actual throttle opening degree detected by the throttle opening degree sensor 19 and the target throttle opening degree, and controls the intake quantity such that the opening degree of the throttle valve 12 follows the target value, thereby controlling the engine to the target torque T.sub.er.
The ECU 6 calculates a speed ratio e (=N.sub.t /N.sub.E) of a torque converter from a speed ratio of the rotation speed N.sub.t of an output shaft of the torque converter as compared to the rotation speed N.sub.E of the engine, reads a torque ratio f of the torque converter from a predetermined torque ratio map as a function of the speed ratio e of the torque converter, and calculates the torque T.sub.t of the output shaft of the torque converter from the torque ratio f and the target engine torque T.sub.er based on the following equation (5). EQU T.sub.t =f.multidot.T.sub.er ( 5)
Furthermore, the ECU 6 reads a target speed changing step from a predetermined shift pattern schedule table by the vehicle speed V.sub.sp detected by the vehicle speed sensor 63 and the torque T.sub.t of the output shaft of the torque converter, and performs the speed changing control wherein the operational combination of the hydraulic friction engaging elements is switched by outputting a control signal of an ON-OFF logic in accordance with the target speed changing step, to a shift solenoid valve in the hydraulic control unit 5a of the automatic transmission 4 such that the gear speed changing unit 43 is shifted from a current speed changing step to the target speed changing step.
As other conventional technology, hydraulic wet clutches or brakes employed in the automatic transmission which conventionally achieves plural steps of gear changing ratios by a selective combination of a plurality of gears, performs engaging and disengaging of the transmission torque by supply and discharge of a hydraulic pressure called line pressure.
Generally, this line pressure is controlled by regulating a spool opening degree by a set pressure and a feedback pressure in the axial direction of a pressure regulating valve employing a spool valve, and is set in accordance with the speed changing step and the output of the engine, for instance, increase of the throttle opening degree.
Furthermore, setting the line pressure based on a pulse width of fuel injection of the engine, has already been considered, which is shown, for instance, in Japanese Unexamined Patent Publication No. 116363/1989. In this conventional example, the pulse width of fuel injection is regarded as approximately proportional to the output torque of the engine, and based on a predicted value of the engine torque, the line pressure of the automatic transmission is regulated.
In the conventional control device for a vehicular engine having an automatic transmission, the output torque of the engine is not detected and the torque T.sub.t of the output shaft of the automatic transmission 4 which is the target in the speed changing operation, is indirectly predicted by calculation from the accelerator opening degree "a" and the rotation speed N.sub.E of the engine. In the speed changing operation, the hydraulic pressure control is not performed in accordance with the torque T.sub.t of the output shaft of the automatic transmission 4. Accordingly, a speed changing shock may be caused by variations, timewise changes or the like of the engine or the hydraulic characteristics of the automatic transmission 4, which brings about a disagreeable feeling to a driver and a favorable shift quality is not provided.
In the line pressure control device in the conventional control apparatus for a vehicular engine, having an automatic transmission, the engine output is predicted without directly detecting the engine torque, the input torque of the automatic transmission is calculated based on an average characteristic of the torque converter, a torque quantity considering a safety factor against a rapid load variation is regarded as the input torque for the automatic transmission, and the line pressure necessary for the torque transmission is calculated by a predetermined method, for instance, a map-look-up, thereby determining the line pressure.
Accordingly, the actually necessitated line pressure is previously determined to a higher value so that disadvantage by, for instance, an excessive slip of the hydraulic wet clutches and brakes, is not caused by individual difference, aging and the like of the engine. Therefore, a driving loss of a pump of the automatic transmission increases, which causes to deteriorate a fuel cost of the engine.
Furthermore, in the conventional example wherein the engine torque is predicted by employing the pulse width of the fuel injection, the accuracy of predicting the torque is deteriorated when the combustion efficiency of the engine changes by the change of the intake quantity or by a warming-up state of the engine, and as a result, the accuracy of controlling the line pressure is deteriorated.